Defibrillation Testing in Patients Undergoing Replacement of the S-ICD Generator: Is There Still a Need?

Background: Noninferiority of omitting intraoperative defibrillation threshold (DFT) testing has been documented for transvenous implantable cardioverter defibrillators (ICD) whereas data for the subcutaneous-ICD (S-ICD) regarding the need for DFT testing, especially during S-ICD generator replacement, is not available.

Methods: A total of 112 consecutive patients who underwent S-ICD generator replacement and routine testing were included in this retrospective single-center study and analyzed regarding the outcome of intraoperative DFT.

Results: The majority of patients (87.3%) were successfully tested during generator replacement with no major adverse events. PREATORIAN score was generally lower, while high voltage (HV) impedance increased compared to first implantation. The risk of conversion failure increased with the PRAETORIAN risk class, whereas patient characteristics did not impact conversion rates. PRAETORIAN score and HV impedance were shown to be the most accurate factors when predicting conversion failure. In all patients with an HV impedance <70 Ohm and a PREATORIAN score < 90 at the time of initial implantation DFT was successfully performed during generator replacement.

Conclusion: General omittance of DFT in S-ICD generator replacement is not advisable. New algorithms for low impedance DFT measurements during S-ICD query and PREATORIAN score at first implantation can be used to predict conversion failure. An impedance <70 Ohm and a PRAETORIAN score < 90 show a very low risk of conversion failure. In patients with a PRAETORIAN score > 150 DFT testing should be performed when the S-ICD generator is replaced until randomized data is available.